ABSORPTION SPECTRUM EXPLORATION

Introduction

In this lab, students will explore
the absorption spectra of standard food colors as found in
grocery stores, then mix different colors together after
predicting what the resulting absorption spectra will resemble.
In the process of doing this lab, the basic principle being
investigated is often termed “color subtraction”.

Materials

Vernier Spectrometer

Standard Food Colors (RYB)

Computer with Logger Pro or
LabQuest*

Water

Cuvettes for Spectrometer

Pipettes (suggested)

*Original LabQuest or
LabQuest 2 can be used.

Procedure

1. Prepare mixtures of the three
basic food colors and water so they are not too dark. Mix 1 drop
per 400 mL water as a good approximation. Fill a cuvette
approximately ? full with each color mixture. Use a cap to
prevent accidental spillage. Keep your extra quantities of your
original mixtures for use later in the lab.

2. Connect the Spectrometer to your computer or LabQuest. Launch
Logger Pro if using computer or the LabQuest app if using
LabQuest. The default in both systems is light absorption.

3. Calibrate your spectrometer using a cuvette filled with
water.

4. One at a time, collect the absorption spectrum of the colored
water. Describe where absorption takes place and how this leads
to the color of the mixture. Store each run and label each with
the color of the mixture. Collect all three and make sure they
are stored before moving on to the next step.

5. Display the graphs for the yellow and blue mixtures. What
happens to the color when you mix yellow and blue? Under
Analyze, choose Draw Prediction and sketch what you think the
graph will look like if you mix your two colors together.

6. Then mix approximately equal amounts of the yellow mixture
with the blue mixture. Making sure you’ve stored all the
previous results, collect a fresh set of data and compare your
prediction with the actual graph.

7. In what ways were you correct and in what ways were you
incorrect? Describe the color of the mixture and graph that
resulted. How does the graph explain the color you observed?